Conjugated diene rubbers (e.g. a styrene-butadiene copolymer) obtained by methods of emulsion polymerization has been known as rubbers for automobile tires. Recently, under circumstances where improvements in low fuel consumption performance of automobiles have been expected, various types of conjugated diene rubber capable of realizing an excellent low fuel consumption performance have been proposed.
As an example, a conjugated diolefin (co)polymer rubber with the following characteristics (1) to (3) and a rubber composition containing the conjugated diolefin (co)polymer have been proposed: (1) it is a (co)polymer rubber of a conjugated diolefin or a conjugated diolefin and an aromatic vinyl compound; (2) it has a primary amino group and an alkoxysilyl group bound to the (co)polymer chain; and (3) a di- or more functional monomer is copolymerized in the (co)polymer chain, and/or, at least a portion of the (co)polymer chain is coupled with an di- or more functional coupling agent (Patent Document 1).
As another example, a modified diene polymer rubber that is obtained by a step 1 of obtaining an active polymer having an alkali metal end by polymerizing a conjugated diene monomer or a conjugated diene monomer and an aromatic vinyl monomer in a hydrocarbon solvent in the presence of an alkali metal catalyst and a step 2 of obtaining a modified polymer rubber by reacting the active polymer with a compound that is represented by a specific formula, and a rubber composition containing the modified diene polymer rubber have been proposed (Patent Document 2)
In addition, as a method for producing a modified polymer capable of increasing interactions with silica and carbon black to improve fracture characteristics, abrasion resistance and low-exothermic properties, there have been proposed a method of performing a primary modification reaction in which a polymer having an organometallic active site in the molecule is reacted with a hydrocarbyloxysilane compound at the active site and performing a subsequent secondary modification reaction in which the hydrocarbyloxysilane compound is further reacted via a condensation reaction between hydrocarbyloxysilyl groups, and a rubber composition containing the modified polymer obtained by the method (Patent Document 3).